This invention relates to means for bending sheet or like material which precludes damage to the part being formed.
In today's industrial operations many parts are formed in a stamping operation in a press. For such purpose the press is provided with the required set of tools and dies. The tools and dies are appropriately mounted to the ram or the bed of the press and one thereof is reciprocated relative the other as sheet or like material, from which a part is being formed, is fed therebetween. In many instances one or more of the mating tools and dies is designed to bend, from the plane thereof, a portion of the sheet material. In accordance with prior art practice, mating tool and die elements used for such purpose are so arranged that the bending tool is a rigid punch-like element mounting perpendicular to the sheet material. In most cases this rigid element has an operating surface including a portion which, as the press is operated, moves in a vertical plane adjacent and parallel to a cooperating surface of a related forming die. An inherent result of its use is the production of shear forces having side effects tending to damage, and in some cases irreparably damage, the part being formed.
Another undesirable effect of using bending apparatus of the prior art is that the nature thereof and the manner of its application is such to introduce residual stresses in the displaced portion of the sheet material. This results in "springback." When this occurs, as is often the case, a secondary forming operation is required to return the displaced portion of the sheet material to the position in which it must be set.
The incidence and degree of springback is particularly difficult to anticipate. This is due to the fact that it depends both on the ratio of the bend radius to the thickness of the stock to which the bend is applied and the tensile strength and unit elongation of the material being bent. As a result for the most part, the design of tooling for bending procedures has been a matter of trial and error, with no guarantee as to results.
In any event, it has been found the bending of portions of sheet material usually requires a secondary forming operation due to the springback. One such secondary forming operation is commonly called "side cam tooling." Another is called "coining." Either operation adds to the forming costs and incurs the possibility of causing undesirable thinning and stressing of the formed material.
Thus, in accordance with prior art practice bending is not engineered but merely contrived, in a relatively uneconomical fashion, and with means and methods lacking the characteristics of precision and oftentimes producing rupturing, skidding and stretching of the sheet material to which the operation is applied.
In some cases use of the prior art apparatus dictates that the press employed must have a higher tonnage than would normally seem reasonable. Die costs are also increased since the bending operation in accordance with prior art practice necessitates substantial anchoring means to offset the possibility of a skidding of sheet material on which the bending operation is being performed.